// check if its a convert_from or convert_to function
if (functionName.equalsIgnoreCase("convert_from") || functionName.equalsIgnoreCase("convert_to")) {
assert nArgs == 2 && function.getOperands().get(1) instanceof RexLiteral;
String literal = ((NlsString) (((RexLiteral) function.getOperands().get(1)).getValue())).getValue();
RexBuilder builder = new RexBuilder(factory);
// construct the new function name based on the input argument
String newFunctionName = functionName + literal;
// Look up the new function name in the drill operator table
List<SqlOperator> operatorList = table.getSqlOperator(newFunctionName);
assert operatorList.size() > 0;
SqlFunction newFunction = null;
// Find the SqlFunction with the correct args
for (SqlOperator op : operatorList) {
if (op.getOperandTypeChecker().getOperandCountRange().isValidCount(nArgs - 1)) {
newFunction = (SqlFunction) op;
break;
}
}
assert newFunction != null;
// create the new expression to be used in the rewritten project
newExpr = builder.makeCall(newFunction, function.getOperands().subList(0, 1));
rewrite = true;
}
}
exprList.add(newExpr);
}